This invention generally relates to multiple voltage regulators in a single integrated circuit package. In particular, it relates to voltage regulators used for providing regulated voltage to telephone subscriber circuits.
The power for the operation of a telephone is provided over the same telephone lines which provide the signaling and the voice or data communications. Typically, this power is provided at the local switching center, and may be provided by a storage battery or other source of direct current voltage. Since a number of subscriber lines derive their power from a common source, variations in the loading on the source caused by fluctuations in the use of the telephone service by the subscribers can result in unacceptable variations in the voltage provided to the subscribers. Thus, it is customary practice to provide voltage regulators to control the voltage provided to each subscriber.
Although the voltage regulator for each subscriber can be provided as a separate device, the cost of doing so would be prohibitive when compared with the cost of using multiple regulators in a single integrated circuit device. However, when multiple devices are included in one circuit, problems with one regulator in the integrated circuit can cause all of the regulators in the circuit to become inoperable. For example, a short circuit on the output of one regulator can cause the temperature of the integrated circuit to increase to an unacceptable temperature and cause the failure of the entire circuit. Thus, a problem with one subscriber line can cause the failure of all subscriber lines associated with the integrated circuit package. For this reason, prior art devices have turned off all the regulators in the circuit if an over-temperature condition occurs. Although this protects the other circuits from damage, it also unnecessarily interrupts the power to the subscribers served by the other regulators.
Therefore, a need exists for providing a plurality of voltage regulators in one integrated circuit device with a means for sensing temperature, and an ability to independently disable the one voltage regulator which is causing the over-temperature condition, thus, allowing the remaining voltage regulators to continue to operate.